I painted mine on my 01 Silvy. Mu truck is black with a lot of chrome, including a billet grill insert. I decided to black out the entire front as the billet was getting kinda dull.
1st thing I did wad remove the grille completely and power washed it front and back. If you dont have a power washer you can use a stream sprayer on your water hose. I let it dry and removed my billet inserts to paint separately.
Then use some 800 grit wet/dry sandpaper to de-gloss the areas you'll be painting. It doesn't take much sanding, you just want to "rough up" the surface a bit. I then have the whole grille a rub down with denatured alcohol to remove any dust and oils left over.
Mask off any areas that aren't going to be painted, then spray the grille with adhesion promoter following the directions on the can. This will really help the paint stick and help prevent chipping and peeling. After that I used Krylon Fusion gray primer in several light coats. After the 4th coat I lightly sanded the primer with 2000 grit wet/dry sandpaper before applying the finish coat.
For the finish coat I used Krylon Fusion gloss black, also in several light coats about 3 minutes apart. I let the grille dry overnight, then applied Krylon high gloss clear coat. What I have found works best on the clear coat is 2-3 light coats about 5 minutes apart, then wait about 10 minutes and apply a heavy "wet" coat. After that don't do anything else to it, move it or anything for at least 1 hour. Although the clear coat dries in about 10 minutes, give it the extra time to harden a bit, which it will continue to do for about 10 days.
Hope this helps!